Friday Headlines, November 7, 2014
THE LATEST IN THE GEOSCIENCES
A Rare Mineral Found in Meteor Craters
Iapetus was the Impetus
A Pregnant Eocene Mare
There are two things significant here.
One is the mineral itself, which is known only from ancient meteorite impacts. Reidite is a form (a polymorph) of a more common mineral found on Earth called zircon. Zircons are commonly used in radiometric dating methods to assign an age to rocks. This particular form of zircon forms only under conditions of high pressure.
The other significant thing is the crater. The Rock Elm Crater formed when an impact happened between 450 and 470 million years ago, right in Wisconsin. But you could easily drive right through the town of Rock Elm and never know there was a crater there. That’s because erosion has completely beveled the surface flat.
So how do we know there is even a crater there? Geology of course.
There is an obvious circular structure formed by small faults in the region:
The different colors are different kinds of rock that were brought into contact with each other due to the force of the impact.
The Phanerozoic Era (the Era of Visible Life) began about 540 million years ago. The point marks the beginning of the Cambrian Period and the end of the Precambrian Era.
During the Cambrian, almost all of the diversity of major groups of organisms formed, everything from the lowly sponge to chordates – our own lineage – and everything in between, including worms, crabs, and clams. This event is called the “Cambrian Explosion” that occurred over a few 10s of millions of years.
One question that paleontology and geology have been working on is ‘why’? Why did this diversification suddenly happen? Why then?
Geologists already agree that sea level was rising at that time. Atmospheric oxygen was also on the increase, and ocean chemistry was changing.
Where they don’t agree, necessarily, is with the timing of the formation of the Iapetus Ocean.
It was previously thought that the ocean formed much earlier than the Cambrian Explosion.
The new research by scientists at the University of Texas at Austin shows that the opening of Iapetus coincides with the Cambrian Explosion, perhaps itself being a key player in the diversity of life on Earth.
In the category of “Wow, that’s cool,” this week researchers at the Society of Vertebrate Paleontology Annual Meeting in Berlin presented a newly described specimen of the ancient horse Eurohippus messelensis. This early horse (which hardly looked like a horse as it had multiple hoofed toes on all its feet and was very small) lived about 47 million years ago, at a time of extreme global warmth.
What’s significant about this specimen is that it is a pregnant female. The fetus was very close to full term, as evidenced by its nearly fully mineralized teeth. The foal was not in a birth position, so researchers believe that this mare did not die during birth. The actual cause of death is unknown.
What’s more, some of the uterine tissues are preserved, which is a very exciting find given that soft tissues aren’t often preserved.